Remove default value checking in GN, adds getenv function, reorders parameters to rebase_path.

tools/gn/value.cc

Index: tools/gn/value.cc
diff --git a/tools/gn/value.cc b/tools/gn/value.cc
index b36c962516fbddb1babfd6e058b1498b3231a1d0..659ebb9bb0b12517864a65e8203bd5a678212ecb 100644
--- a/tools/gn/value.cc
+++ b/tools/gn/value.cc
@@ -8,12 +8,14 @@
 
 Value::Value()
     : type_(NONE),
+      boolean_value_(false),
       int_value_(0),
       origin_(NULL) {
 }
 
 Value::Value(const ParseNode* origin, Type t)
     : type_(t),
+      boolean_value_(false),
       int_value_(0),
       origin_(origin) {
 }
@@ -35,6 +37,7 @@ Value::Value(const ParseNode* origin, int64 int_val)
 Value::Value(const ParseNode* origin, std::string str_val)
     : type_(STRING),
       string_value_(),
+      boolean_value_(false),
       int_value_(0),
       origin_(origin) {
   string_value_.swap(str_val);
@@ -43,6 +46,7 @@ Value::Value(const ParseNode* origin, std::string str_val)
 Value::Value(const ParseNode* origin, const char* str_val)
     : type_(STRING),
       string_value_(str_val),
+      boolean_value_(false),
       int_value_(0),
       origin_(origin) {
 }